The present invention relates to an optical recording material, and more particularly to an optical recording material applicable to the recording layer of a phase-change type optical recording medium, which comprises a solid solution of a stoichiometric compound GeSbTe alloy and a ternary alloy having essentially the same crystal structure with the same stoichiometry as the GeSbTe alloy.
Phase change rewritable optical recording finds its primary applications in rewritable discs of CD (Compact Disc) and DVD (Digital Versatile Disc), two most successful formats of optical discs to date. It is apparent that the phase change technology will uphold future rewritable DVD""s with larger storage capacities and furthermore may prove to be a competitive technology for near-field recording media with recording densities well beyond what are accessible with the diffraction limited optics.
A phase-change rewritable optical recording medium makes use of a recording material which is capable of undergoing reversible phase changes between crystalline and amorphous phases under controlled laser beam irradiation. Information is recorded on the recording layer by way of formation of amorphous marks, is erased therefrom by way of crystallization of the amorphous marks and is reproduced from difference in reflectivity between the amorphous marks and the crystalline areas.
Accordingly, a recording material for a phase change rewritable optical recording medium is required to possess the following properties: the difference in reflectivity between its amorphous and crystalline states corresponding respectively to the recorded and erased states of information, should be large; its melting temperature should not be too high or too low; it can easily form an amorphous state by cooling from a liquid state; the amorphous state should be stable during repeated reproductions and at a use condition; and the crystallization kinetics should be sufficiently fast so that the recorded data can be erased within the limited beam dwell time.
Regarding these properties of phase change recording materials, an important problem may be addressed that is encountered in the quest for a recording medium with a higher recording density and data transfer rate. In optical data storage, increase in recording density and data transfer rate is achieved primarily by means of reduction in laser spot size (d) at the recording medium and/or increase in disc linear velocity (v). By either means, however, the dwell time (d/v) of a laser beam becomes diminished; for example, laser dwell time diminishes by a factor of four providing that laser spot size is reduced by half and linear velocity increased two fold.
Such decrease in beam dwell time may render crystallization of the amorphous marks either incomplete or impossible during erasing of the recorded data, leading to a poor erasibility and overwritability of a recording medium. Among the properties required of a phase change optical recording material, a fast crystallization kinetics becomes then critically important. Stoichiometric compound phase change alloys tend to have faster kinetics of amorphous to crystalline transformation and are considered as good candidates to overcome the problem with.
Tellurium (Te)-based materials, stoichiometric compound GeSbTe alloys in particular, have been utilized as phase-change recording materials for rewritable optical data storage. In order to improve the crystallization kinetics of these alloys for use in recording media with higher recording densities and data transfer rates, efforts have been made to date by way of either of two different approaches: use of a single additive element of various kinds or use of crystallization promoting layers.
For example, U.S. Pat. Nos. 5,100,700 and 6,040,066 and published reports by J. H. Coombs et al. [J. Appl. Phys., 78, 4918 (1995)] and by C. M. Lee et al. [J. Appl. Phys., 89, 3290 (2001)] disclose GeSbTe alloys incorporated by a fourth element of either an interstitial or a substitutional type such as O, Sn or Bi.
Further, U.S. Pat. No. 5,965,229, a published work by N. Yamada et al. [Jpn. J. Appl. Phys., 37(4B), 2104 (1998)] and Korean Laid-open Patent Publication Nos. 97-67128 and 98-11179 disclose a recording medium comprising a crystallization-promoting layer of SiN, SiC or GeN respectively disposed between dielectric and recording layers.
It is an objective of this invention to put forth another approach that could be used to improve the crystallization kinetics of and therefore to extend the utility of the stoichiometric compound GeSbTe alloys, in response to a diminishing beam dwell time due to a progressive increase in recording density and data transfer rate of rewritable phase change optical recording media.
The present invention provides an optical recording material for a rewritable phase-change optical recording medium having high-speed crystallization and excellent erasing properties.
An optical recording material according to the present invention comprises a composition having the formula of:
(AaBbCc)x(GeaSbbTec)1xe2x88x92x 
wherein, A is an element selected from the group IVB of the periodic table; B is an element selected from the group VB of the periodic table; C is an element selected from the group VIB of the periodic table; a, b and c are atomic mole ratios; 0 less than x less than 1, x being a mole fraction; and at least one of A, B and C has a higher atomic number, and thus a smaller diatomic bond strengths than that of the corresponding element in the GeSbTe part.